Global cross-technology analysis of the Hunga Tonga-Hunga Ha’apai explosive eruption from the perspective of CTBT monitoring

The Comprehensive Nuclear-Test-Ban Treaty prohibits all nuclear explosions. For detection of potential non-compliance, the International Monitoring System with 321 stations is being installed and largely completed. Seismic, hydroacoustic and infrasound stations detect, localize and characterize explosions. Highly sensitive radionuclide stations sniff for radioactive traces potentially released from nuclear explosions. The International Data Centre (IDC) in Vienna processes the IMS data and generates several standard data analysis products for distribution to the member states. However, the judgement on the character of potentially treaty relevant events it is the sole responsibility of the State Signatories. Therefore, National Data Centres (NDC) are established in many states. The German National Data Centre is hosted by BGR and supported by BfS (Federal Office for Radiation Protection) with radionuclide expertise. Furthermore NDCs can use additional observation data sources other than recorded by the IMS like national stations or remote sensing data. There have been several larger test cases for the verification system as the announced nuclear tests in the DPRK 2006-2017, the Fukushima-Daiichi radionuclide emissions 2011, the Chelyabinsk meteorite 2013 or the accidental explosion in Beirut 2020.

Recently, the very large eruption of the Hunga Tonga Hunga Ha’apai volcano occurred on January 15^th 2022 in the South Pacific Ocean and turned out to be a strong source of waveform phenomena in solid earth, water and atmosphere.

Seismic PKP phases travelling through the core of the Earth were the first seismic signal of the event registered at German IMS station PS19 and the national Gräfenberg array. A preliminary moment tensor inversion analysis for P- and S-Phases shows the mainly explosive character of the event. Sensors of the hydro-acoustic component of the IMS also recorded the main eruption as well as ancillary volcanic activity at the two hydrophone arrays in the Pacific Ocean up to nearly 10000 km distance. The eruption caused a long period atmospheric pressure wave even measurable with classical barometers and pressure sensors in smartphones around the globe. Consequently, all 53 certified IMS infrasound stations detected signals from the event. Recurrent infrasonic signatures travelled around the globe several times and were recorded by IMS stations in the following days. The eruption was presumably the strongest infrasound source since installation of the IMS started.

Finally, the atmospheric sensitivity of the IMS radionuclide stations to hypothetical releases connected with the eruption is investigated by means of Atmospheric Transport Modelling. The results show threshold values for detectable releases of radioactive fission and activation products.

Overall, the very huge volcanic eruption can serve as upper benchmark event for the CTBT compliance monitoring capability using cross-technology analysis of IMS data.